This invention relates to the use of a screening method for the selection of mutations which confer acetohydroxy acid synthase inhibiting herbicide resistance to wheat. This invention also relates to the resistant wheat developed by this method.
The first enzymatic step common to the biosynthesis in plants of the branched chain amino acids (valine, leucine and isoleucine) is catalyzed by the enzyme acetohydroxyacid synthase (AHAS; also known as acetolactate synthase; E.C.4.1.3.18). AHAS catalyzes two parallel reactions: condensation of two moles of pyruvate to give rise to acetolactate, and condensation of a mole of pyruvate and a mole of alpha ketobutyrate to yield acetohydroxybutyrate. This enzyme is inhibited by the end products of the pathway (valine, leucine and isoleucine) and this is one of the known mechanisms of regulation of this pathway in higher plants.
AHAS is the target site of several classes of structurally unrelated herbicides. These herbicides include the imidazolinones, the sulfamoylureas, the sulfonylcarboxamides, the sulfonamides and the sulfonylureas.
Large scale commercial agriculture relies heavily on row-crop production practices. The availability of herbicides which selectively eliminate problem weeds while leaving crop plants undamaged is a major enabling component of these practices. Herbicides which control the majority of problem weeds are available for most major crops. The afore-mentioned AHAS inhibiting herbicides are a key element in weed control. These same herbicides, however, may miss important weeds in certain niche crop production areas. Also, currently used herbicides may have ecological problems or cost constraints attached to their use.
There is a need to develop varieties of wheat which are resistant to AHAS inhibiting herbicides. The development of such resistant varieties would permit wheat growers to use the AHAS inhibiting herbicides, whose use results in reduced application rates, reduced ground water contamination and reduced animal toxicity when compared to other classes of herbicides.
Accordingly, it is an object of this invention to develop a screening method for the selection of mutations which confer AHAS inhibiting resistance to wheat.
It is a particular object of this invention to develop a screening method for the selection of mutations which confer AHAS inhibiting imidazolinone herbicide resistance to wheat.
It is an additional object of this invention to identify wheat selections identified by the novel screening method.
These objects are accomplished by mutagenizing wheat seeds with a chemical mutagen. In a first screening step, seeds are soaked in an AHAS inhibiting herbicide-containing solution. In a second screening step after planting, soil containing the seeds is sprayed with an AHAS inhibiting herbicide prior to the emergence of seedlings from the soil. Those wheat seedlings which emerge demonstrate resistance to AHAS inhibiting herbicides.